The present invention relates to a mass sensor for determining a minute mass of a nanogram (10xe2x88x929 g) order, for example, a mass sensor for sensing microorganisms such as bacteria, viruses, and protozoa (immune sensor), and a mass sensor for sensing moisture, toxic substances, or specific chemical substances such as taste components (moisture meter, gas sensor, and taste sensor), and a method for sensing a mass. In particular, the present invention relates to a mass sensor, and a method for sensing a mass, conveniently used for determining the mass of a body to be sensed by measuring change in resonant frequencies caused by changes in the mass of the diaphragm on which a catching substance for catching a body to be sensed by reacting only with the body to be sensed is applied.
Since the mass sensor of the present invention is not limited to the measurement of change in the mass of the catching substance applied on a diaphragm as described above, that is, not limited to the indirect measurement of change in the mass of a diaphragm, but it is naturally possible to sense change in resonant frequency due to change in the mass of the diaphragm itself, the mass sensor can also be used as a thickness meter for vapor-deposited films or a dew point meter.
Furthermore, even if the mass of the diaphragm is not changed directly or indirectly, the mass sensor of the present invention can also be used as a vacuum meter, a viscosity meter, or a temperature sensor by placing it in an environment to cause change in resonant frequency, that is, by placing it in an environment of medium gases or liquids having different degrees of vacuum, viscosity, or temperature.
Thus, although the mass sensor of the present invention can be used in various applications depending on its embodiments, the same basic principle is also applied to the measurement of change in resonant frequencies of the diaphragm and the resonating portion including the diaphragm.
Recent progress of scientific and medical technologies, and newly developed medicines such as antibiotics and chemicals have enabled the treatment of various diseases heretofore considered to be difficult to treat. On the other hand, especially in developed countries where people are accustomed in such medical civilization, immunological resistance of human beings have lowered, and many people have suffered from various diseases caused by substances or microorganisms which heretofore had not hurt human beings.
Among what are referred to as diseases, microorganism examinations are essential for the treatment of diseases caused by microorganisms such as bacteria, viruses, or protozoa, to find their pathogens, to clarify their types, and to determine drugs to which they are sensitive.
At present, in the first stage of microorganism examinations, since the cause of a disease and the type of the pathogen can be estimated from the symptoms, various specimens, such as blood, are selected depending on the type of the disease, pathogens present in the specimens are morphologically identified, or antigens or the specific metabolites of pathogens (e.g., toxins or enzymes, etc.) existing in the specimens are immunochemicaly identified. This process is smear, tinction, or microscopy used in bacterial examinations, and in recent years, instantaneous identification has become possible in this stage by fluorescent antibody tinction or enzymatic antibody tinction.
Furthermore, the virus serological test, recently used in the detection of viruses, is a method for proving the presence of specific immunity antibodies that appear in the serum of a patient. Examples of the method include the complement fixation reaction in which the presence of antibodies or antigens is determined by adding complements to test blood, and by observing whether the complements react with antigens or antibodies in the blood and fix to the cell membranes of the antigens or antibodies, or destroy the cell membranes.
Except extremely special cases where symptoms have not been seen heretofore, and the disease is caused by a new pathogen which has not been discovered, in the treatment of diseases caused by microorganisms or the like, adequate treatment can be conducted by finding pathogens in an early stage through the microorganism test described above, and the patient can be led to recovery without worsening of the symptoms.
However, with methods such as smear, tinction, and microscopy, the detection of microorganisms is often difficult depending on their quantities, and time-consuming treatment such as the culture of specimens on an agar is required at need. Also in the virus serological test, since measurements must be performed as a rule during both the acute stage and the convalescent stage for determination from the movement of the quantities of antibodies, there is the problem of time consumption from the point of view of prompt diagnosis.
As seen in complement fixation described above, when a substance to be sensed reacts with a catching substance which catches the substance to be sensed by reacting only with specific substance to be sensed, microorganisms, the mass of the catching substance increases by the mass of the substance to be sensed, even slightly. Such an increase in the mass similarly occurs in the relationship between a catching substance and a chemical substance such as a specific gaseous substance and a smell component, and also applies to the case where a substrate itself without change in the mass is a catching substance, on which a specific substance is deposited or added. On the contrary, when a reaction in which a substance to be sensed caught by a catching substance or the like is released occurs, the mass of the catching substance or the like slightly decreases.
As an example of a method for sensing change in such a small mass, U.S. Pat. No. 4789804 discloses in FIG. 27 thereof a mass sensor 80 comprising a quartz oscillator 81 and electrodes 82, 83 facing the quartz oscillator. When any substance adheres externally on these electrodes 82, 83, the mass sensor 80 senses change in their mass using change in the resonant frequency of the thickness slip oscillation of the quartz oscillator 81 in the direction of the surface of the electrodes. Since such a mass sensor 80 measures change in resonant frequency basically caused by change in the mass load on the quartz oscillator 81, such a mass sensor 80 is considered to be able to be used also as a thickness meter for measuring the thickness or the growth of a vapor-deposited film, or a moisture meter.
However, when such a quartz oscillator 81 is used, since the part on which an external substance adheres and the part for detecting resonant frequency are in the same location, for example, the resonant frequency is unstable when the piezoelectric properties of the mass sensor 80 itself vary due to the temperature of the specimen or change in temperature. Also, if the specimen is a conductive solution, and when the mass sensor 80 is immersed unprotected in the specimen, a short-circuit between electrodes may occur. Therefore, the mass sensor 80 must be subjected to insulation such as resin coating.
The present invention aims to solve the above problems of a micro-mass sensor, and according to the present invention, there are provided first to sixth mass sensors described below.
As a first mass sensor, there is provided a mass sensor characterized in that a piezoelectric element is arranged on at least a part of at least one plate surface of a sensing plate, a side of at least one sheet-like diaphragm is joined to a side of said sensing plate so that the plate surface of said diaphragm is perpendicular to the plate surface of said sensing plate, the other side of said sensing plate is joined to a sensor substrate, and a resonance portion is formed of said sensing plate, said diaphragm, and said piezoelectric element.
Furthermore, as a second mass sensor, there is provided a mass sensor characterized in that a connection plate is joined to a diaphragm at respective sides, a sensing plate is joined to said connection plate at respective sides in the direction perpendicular to the joining direction of said diaphragm and said connection plate, a piezoelectric element is arranged on at least a part of at least one of the plate surfaces of said sensing plate, at least a part of sides of said connection plate and said sensing plate is joined to a side of the sensor substrate, and a resonance portion is formed of said diaphragm, said connection plate, said sensing plate, and said piezoelectric element.
Furthermore, as a third mass sensor, there is provided a mass sensor characterized in that a connection plate is joined to a diaphragm at respective sides, two sensing plates are joined to said connection plate at respective sides in the direction perpendicular to the joining direction of said diaphragm and said connection plate so as to sandwich said connection plate, a piezoelectric element is arranged on at least a part of at least one of the plate surfaces of at least one of said sensing plates, at least a part of sides of said connection plate and said sensing plates is joined to a side of the sensor substrate, and a resonance portion is formed of said diaphragm, said connection plate, said sensing plates, and said piezoelectric element.
Here, in the third mass sensor, it is preferable that said piezoelectric element is arranged on at least one of the plate surfaces of one of said respective sensing plates facing to each other via the connection plates, and one or more, preferably a plurality of, slits are formed on the other sensing plate in the direction perpendicular to the joining direction of said other sensing plate and said connection plate. It is also preferable that respective piezoelectric elements are arranged on the plate surfaces of said respective sensing plates facing to each other via the connection plates in at least the same direction, and that the polarizing direction of the piezoelectric film in said piezoelectric elements arranged on one of the sensing plates, and the polarizing direction of the piezoelectric film in said piezoelectric elements arranged on the other sensing plate are opposite to each other with respect to the connection plates.
Next as a fourth mass sensor, there is provided a mass sensor characterized in that a connection plate and a sensing plate not directly joined to each other are joined to said diaphragm at respective sides so that the joining directions with the diaphragm are parallel to each other, said connection plate and said sensing plate are joined to one side of a sensor substrate, a piezoelectric element is arranged on at least a part of at least one of the plate surfaces of said sensing plate, and a resonance portion is formed of said diaphragm, said connection plate, said sensing plate, and said piezoelectric element.
As a fifth mass sensor, there is provided a mass sensor characterized in that an assembly of a diaphragm sandwiched with two connection plates by joining at respective sides is placed across the side surfaces of a depression formed on a sensor substrate, each of two sensing plates is placed across said connection plate and across the bottom side of said depression in the direction perpendicular to the direction of said respective connection plates sandwiching said diaphragm, a piezoelectric element is arranged on at least a part of at least one of the plate surfaces of said sensing plates, and a resonance portion is formed of said diaphragm, said connection plate, said sensing plates, and said piezoelectric element.
Here, a depression means that formed from sides facing to each other and the bottom side connecting such sides; however, in the present invention, the bottom side is not necessarily a plane, but the shape of the bottom side may be changed variously unless the measurement of the oscillation and the resonant frequency of the diaphragm, such as the provision of a depression or a projection in the bottom side, is affected.
As a sixth mass sensor, there is provided a mass sensor characterized in that an assembly of a diaphragm sandwiched with two connection plates by joining at respective sides is placed across a through-hole formed on a sensor substrate, at least a plurality of sensing plates are placed between said respective connection plates and the side of said through-hole, or said diaphragm and the side of said through-hole, in the direction perpendicular to the direction of said respective connection plates sandwiching said diaphragm, a piezoelectric element is arranged on at least a part of at least one of the plate surfaces of at least one of said sensing plates, and a resonance portion is formed of said diaphragm, said connection plates, said sensing plates, and said piezoelectric element.
Here, in the sixth mass sensor, when the piezoelectric element is arranged on at least one of the plate surfaces in each pair of said respective sensing plates facing to each other via the connection plates or the diaphragm, it is preferable that one or more, preferably a plurality of, slits are formed on the other sensing plate in the direction perpendicular to the joining direction of said other sensing plate and said respective connection plates. Also, when respective piezoelectric elements are arranged on the plate surface of each pair of said respective sensing plates facing to each other via the connection plates or the diaphragm in at least the same direction, it is preferable that the polarizing direction of the piezoelectric film in said piezoelectric elements arranged on one of the sensing plates, and the polarizing direction of the piezoelectric film in said piezoelectric elements arranged on the other sensing plate is opposite to each other with respect to the connection plates or the diaphragm.
In these second through sixth mass sensors, it is preferable that the diaphragm, the connection plate, and the sensing plate form a same plane when joined to each other, that is, these members have almost the same thickness. It is also preferable that the sensing plate is fitted in and joined to the depression formed by the connection plate and the sensor substrate. It is preferable for this that the diaphragm, the connection plate, and the sensing plate are integrally formed from a diaphragm, and the sensor substrate is laminated integrally with the diaphragm and the base plate.
It is also preferable that a spring plate is bonded to one of or each of plate surfaces of the connection plate, and this spring plate is joined to the sensor substrate or the spring plate reinforcement. At this time, unlike the structure bonded using adhesives, it is preferable that the spring plate is integrally formed with an intermediate plate integrally inserted between the diaphragm and the base plate, or integrally formed with the spring plate reinforcement integrally formed with the diaphragm, and also integrally formed with the connection plate. When a plurality of connection plates are used, it is preferable that the assemblies of the connection plate and the spring plate have the same shape. It is also preferable that the mass sensor has a reinforcing plate joined to the side of said sensor substrate, and in this case, it is preferable that the reinforcing plate is integrally formed with the spring plate and the sensor substrate.
Since a catching substance reacting only with a substance to be sensed and catching the substance to be sensed is applied on the diaphragm, the piezoelectric element measures change in the resonant frequency of the resonating portion in the state when the substance to be sensed has not been caught by the catching substance, and in the state after the substance to be sensed has been caught by said catching substance, all the mass sensors according to the present invention are suitably used in applications to measure the mass of the substance to be sensed caught by the catching substance.
It is preferable that at least two resonating portions are placed on the sensor substrate, and the catching substance is not applied to one of the diaphragm of the resonating portions to use this diaphragm for referencing. On the other hand, it is also preferable that different catching substances are applied to each resonating portion, that is, a plurality of resonating portions to which more than one of different catching substances are separately applied are provided in a sensor. Here, more than one resonating portion may be placed on the sensor substrate so as to expand the dynamic range by integrating the signals from the respective resonating portions. Also, a through-hole of an optional shape may be formed inside said sensor substrate, and the resonating portion may be formed on the internal circumferential surface of the through-hole.
It is also preferable, to improve sensitivity, that one of the piezoelectric element is split into two portions; one is used for driving and the other is used for sensing. Furthermore, it is preferable, to improve sensitivity, that two piezoelectric elements are placed on one resonating portion, and one of the piezoelectric elements is used for driving and the other is used for sensing. Therefore, each of the two piezoelectric elements placed on a resonating portion may be further split into two portions, and in this case, each of the two piezoelectric elements has both driving and sensing functions.
Furthermore, when the specimen is a conductive solution, it is preferable to provide a position sensor consisting of a pair of electrodes on the middle between the diaphragm and the piezoelectric element on the sensor substrate, so that the diaphragm is immersed in the solution but the piezoelectric element is not immersed in the solution even if the mass sensor is immersed, so as to install the mass sensor on a suitable position. Even if the specimen is a conductive solution, the electrodes or other parts can be prevented from short-circuiting, if the piezoelectric element, the electrodes of the piezoelectric element and electrode leads connected to the electrode, are coated with a resin or glass insulation coating layer. Furthermore, it is preferable that a shield layer consisting of a conductive material is formed on the surface of said insulation coating layer, so as to reduce noise such as external electromagnetic waves.
It is preferable that the sensor substrate, diaphragm, connection plate, sensing plate, and spring plate constituting a mass sensor of the present invention are integrally composed of stabilized zirconia or partially stabilized zirconia. As the material for the piezoelectric film in the piezoelectric element, a material containing a component mainly consisting of lead zirconate, lead titanate, and lead magnesium niobate is suitably used, oscillation modes, adjusting the resonant frequencies and sensitivity can be controlled if the shapes of the diaphragm, connection plate, sensing plate, or spring plate are dimensionally adjusted by trimming with laser processing or machining. It is further preferable that the electrode of the piezoelectric element is laser-processed or machined to adjust the effective electrode area of the piezoelectric element.
The term xe2x80x9cpiezoelectricxe2x80x9d used herein includes piezoelectricity and electric distortion, and what are referred to as a piezoelectric element include electric distortion elements, and piezoelectric ceramics include electric distortion ceramics.
Next, according to the present invention, methods for mass sensing corresponding to the structure of various mass sensors as described above are provided. First, there is provided a method for sensing the mass with the mass sensor in which a side of at least one sheet-like diaphragm is joined to a side of said sensing plate so that the plate surface of said diaphragm is perpendicular to the plate surface of said sensing plate on which a piezoelectric element is installed, and the other side of said sensing plate is joined to the sensor substrate, characterized in measuring with said piezoelectric element resonant frequency on the basis of at least either one of, xcex8-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on the perpendicular axis perpendicularly passing through the center of a fixed plane, which is the joining surface of said diaphragm and said sensing plate, in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis, the xcfx86-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on said perpendicular axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis accompanied by the swing in the direction parallel to the side of said diaphragm, or the oscillation of said diaphragm in the direction of said perpendicular axis.
Such a method for mass sensing with a mass sensor is suitably adopted as a method for mass sensing using the first mass sensor according to the present invention as described above from its structure.
Also, according to the present invention there is provided a method for sensing the mass with the mass sensor having at least one piezoelectric element, in which a connection plate is joined to a diaphragm at respective sides, at least one sensing plate is joined to said connection plate at respective sides in the direction perpendicular to the joining direction of said diaphragm and said connection plate, and at least a part of sides of said connection plate and said sensing plate is joined to a part of sides of the sensor substrate, characterized in measuring with said piezoelectric element resonant frequency on the basis of at least either one of, the xcfx86-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on the perpendicular axs perpendicularly passing through the center of a fixed plane, which is the joining surface of said connection plate and said sensor substrate, in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis, or the xcfx86-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on said perpendicular axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis accompanied by the swing in the direction parallel to the side of said diaphragm.
Such a method for mass sensing with a mass sensor is suitably adopted as a method for mass sensing using the second and third mass sensors according to the present invention as described above from their structures.
Furthermore, according to the present invention there is provided a method for sensing the mass with the mass sensor having at least one piezoelectric element, in which an assembly of a diaphragm sandwiched with two connection plates by joinmg at respective sides is placed across the side surfaces of a depression or across a through-hole formed on a sensor substrate, at least a plurality of sensing plates are placed between said respective connection plates and the bottom side of said depression or the side of said through-hole, or between said diaphragm and the bottom side of said depression or the side of said through-hole, in the direction perpendicular to the direction of said respective connection plates sandwiching said diaphragm, characterized in measuring with said piezoelectric element resonant frequency on the basis of at least either one of, the xcex8-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on the perpendicular axis perpendicularly passing through the center of a fixed plane, which is the joining surface of said connection plate and said sensor substrate, in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis, the xcfx86-mode swing oscillation of said diaphragm in which said diaphragm makes pendulum-like oscillation centered on said perpendicular axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis accompanied by the swing in the direction parallel to the side of said diaphragm, the swing oscillation of said diaphragm centered on said perpendicular axis, oscillating in parallel to the direction perpendicular to the side of said diaphragm and also perpendicular to said perpendicular axis, or the rotating oscillation of said diaphragm in the plate surface of said diaphragm.
Such a method for mass sensing with a mass sensor is suitably adopted as a method for mass sensing using the fifth and sixth mass sensors according to the present invention as described above from their structures, and also suitably adopted as a method for mass sensing using the fourth mass sensor having a structure in which the sensing plate also functions as the connection plate.
According to a mass sensor of the present invention, as described above, change in a minute mass occurring in a diaphragm can be known accurately in a short time from a specific value of change in the resonant frequencies of the resonating portion provided in the mass sensor, and the mass sensor has an advantage of easy measuring operation. Therefore, by placing the mass sensor in an environment changing the resonant frequencies of the resonating portion, various physical and chemical quantities can be measured. For example, the mass sensor of the present invention can be used suitably as a thickness meter for vapor-deposited films and a dew point meter; which utilize direct change in the mass of the diaphragm, a vacuum meter, viscosity meter, and temperature sensor, which utilize the environment where the diaphragm is placed, such as vacuum, viscosity, and temperature; and especially, for the identification of a substance to be sensed and the measurement of its mass by applying to the diaphragm a catching substance which selectively reacts with the substance to be sensed such as a microorganism or a chemical substance in a specimen, and by utilizing change in the mass of such a catching substance.